Long-term monitoring of physiological parameters has been particularly problematic to implement. This type of monitoring may be essential in many situations, especially for patients that exhibit transitory physiological abnormalities. The implementation of long-term monitoring can help solve several problems for at-risk patient care such as: 1) allows continuous monitoring, alerting care givers and patients to potential problems while patients are away from a managed care setting; 2) allows true baselines to be obtained, making deviations easier to detect; and 3) allows the automatic collection of important data necessary to determine the efficacy or non-efficacy of therapeutic treatments.
Long-term monitoring is typically easier to accomplish for non-ambulatory patients. There are many examples of devices that monitor physiological parameters in a hospital setting such as electrocardiograms, electroencephalograms, pulse, heart rate, blood pressure, and so on. However, for individuals that lead an active life, very few options presently exist for long-term monitoring of physiological conditions. Most devices only measure periodically and are prone to measurement variations caused by technique, compliance or use. Most often, these devices require a professional to operate and monitor the condition of the device, as well as to assure patient compliance in order to maintain proper functioning of the monitoring instrument. In addition, biocompatibility issues with many of these external devices are numerous, with side effects such as attendant skin irritations, increasing patient non-compliance with the monitoring devices.
Invasive devices can also introduce complications. Although non-compliance and measurement variation issues may be decreased with semi-permanent implantable sensors, biocompatibility issues are even higher. Implantable devices often have a shortened half-life, due to rejection of the device in the patient, accumulation of biological materials on the device themselves or other events, including infection and mechanical breakdown of the device. U.S. Pat. No. 6,092,530 provides a sensor on the implantable device, which monitors accumulation of biological material on the sensor itself, decreasing the need to investigate the state of the device through invasive measures. The sensor is remotely interrogated by an external device via electromagnetic or high-frequency radio waves, triggering the sensor to transmit encoded data to the external reader device.
Other medical sensors have been described which measure various physiological parameters for remote monitoring. For example, U.S. Pat. No. 5,987,352 to Klein, et al. discloses a minimally invasive implant coupled with a telemetry system that stores triggered electrocardiogram data. This device records physiological events that meet a set threshold parameter, which is subsequently downloaded to an external reader device through external interrogation. U.S. Pat. No. 5,833,603 to Kovacs et al. provides a device for monitoring various physiological parameters and storing identified data. Similarly, U.S. Pat. No. 4,854,328 to Pollack discloses an animal monitoring system, which comprises an implantable temperature sensor, and transmitter, which transmits a signal, upon sensing a predetermined threshold value, to a remote receiver. Because the devices record only data that satisfies a set threshold parameter, it is unsuitable for establishing baseline patterns necessary in detecting low frequency events. Both devices also require an external interrogator device, which prompts the transponder to download collected data to an external recording device.
Other wireless technologies enable measurement of various physiological parameters on externally-based or implanted biosensors. U.S. Pat. No. 5,511,553 to Segalowitz also discloses a device which measures multiple electrophysiological parameters that provide continuous monitoring in a wireless fashion for assessment of cardiovascular condition in ambulatory patients. U.S. Pat. No. 6,175,752 to Say et al. discloses an analyte monitor which measures multiple physiological parameters and provides for continuous monitoring in a wireless fashion. The device also provides for a drug-delivery system to alter the level of the analyte based on the data obtained using the sensor. Although both devices combine the use of biological sensors with wireless transmission of data, it does not appear that they provide for a long-lasting, biologically compatible system that allows continuous feedback and analysis with a network-based system capable of relaying information from remote sensors on a mammlian subject to a central data analysis system. There exists a continuing need for long-term physiological monitoring devices that provide sensors which reduce biocompatibility issues and provides a wireless data-relay system which reliably transmits bioparameter data, allowing continuous or periodic monitoring of a patient's or users physiological state.